1. Field of the Invention
The present invention relates to microemulsions of edible oils in a matrix of water and certain alcohols with the aid of certain surfactants.
2. Description of the Prior Art
The microemulsions in question are emulsions formed from water, alcohol, oil, and one or more emulsifying agents or surfactants wherein the individual emulsified particles of oil are so small, they are not visible, even when viewed in an optical microscope. The emulsified particles in such emulsions have a particle size of about 100 to 600 A, "Emulsions: Theory & Practice," 2nd Edition, P. Becher, Reinhold Pub. Corp. NY, NY, 1965, at page 297. Although the individual particles of emulsified oil are not visible under an optical microscope, when the entire microemulsion is subjected to light scattering, some haze or turbidity may be visible depending on the particle sizes of the oil droplets. This light scattering effect of such oil droplets is, however, very weak compared, for example, to the light scattering effect produced by the oil droplets in macroemulsions of milk.
Microemulsions are usually transparent dispersions, usually of water-in-oil (w/o), or oil-in-water (o/w), which are formed spontaneously, without the need for any energy input, when the components thereof are uniformly admixed with each other (S. E. Friberg, J. Dispersion Science & Technology, Vol. 6, No. 3, pages 317-337, 1985). Although such microemulsions form spontaneously when they form, the selection of the components therefor, and amounts thereof, are very critical in order to, first, obtain such a microemulsion, and, second, obtain such an emulsion which is stable for any reasonable period of time (Friberg, supra, at page 320). Based on Friberg's studies, short chain alcohols such as isopropanol, which are too soluble in the aqueous phase, are not useful as cosurfactants in oil-in-water microemulsions (Friberg, supra, page 325).
U.S. Pat. No. 4,146,499 also discloses the use of C.sub.5 -C.sub.16 fatty alcohols as primary surfactants, and C.sub.4 -C.sub.10 tertiary alcohols as secondary surfactants, in the manufacture of certain microemulsions while employing certain combinations of oils and the surfactants in a particular, step-wise process for preparing such emulsions. The use of an essential oil in such emulsions is disclosed in Examples 10 and 11 of U.S. Pat. No. 4146499.
In "Increasing The Stability of Vegetable Oil Solutions With The Aid of Monoglycerides and a Cosurfactant", JAOCS, Vol. 62, No. 9, September 1985, pages 1379-1385, A. M. Vesala et al disclose the evaluation of isopropanol, t-butanol, 1-hexanol, sorbitol, 2- ethoxyethanol and 2-butoxyethanol as possible alcohol co-surfactants in microemulsions of rapeseed oil. The microemulsions of A. M. Vesala et al are water-in-oil type emulsions which are made with & without detergents. Vesala et al indicates that sorbitol did not provide any benefits in the emulsions investigated by them.
The alcohols used in these prior art emulsions are, for the most part, not useful, because of toxicity, legal and adverse flavor characteristic reasons, in microemulsions intended for use in food applications.
U.S. Pat. No. 4,568,480 discloses the preparation of microemulsions with oils, which may include flavor oils, with an alkoxylated phenol compound as a sole, or co-, surfactant.
U.S. Pat. No. 4,595,512 discloses the preparation of acid-in-oil or oil-in-acid microemulsions for various non-food, industrial, applications. Several C.gtoreq.4 alcohols are used as cosurfactants in such emulsions.
U.S. Pat. No. 4,404,109 discloses the use of certain N-acyl-.alpha. amino acid salts as surfactants in emulsions that contain aqueous saline solutions. Various alcohols are also disclosed as useful cosurfactants. The prime use for these emulsions is in the field of the tertiary recovery of crude oil.
U.S. Pat. No. 4,605,422 discloses oil-in-alcohol microemulsions useful as lubricating fluids.
Prior to the present invention, therefore, the art had not devised processes or formulas whereby a broad range of edible oils might be placed, in a facile manner, in microemulsions that were entirely composed of components that were of food grade quality, and which were microbiologically and thermodynamically stable for long periods of time under ambient conditions of storage and use.